Field of the Invention. The present invention relates generally to conductive vias for use in circuit boards, semiconductor dice and wafers, interposers, and other substrates. More particularly, the present invention relates to conductive vias that have two or more conductive elements that are spaced substantially the same distance apart from one another as are the conductive traces that electrically communicate with the conductive elements of the via. The present invention also relates to methods for enabling electrical communication between at least two electronic devices using a circuit board using such conductive vias, and to methods for establishing electrical communication between at least two electronic devices through a substrate using such conductive vias.
Discussion of Related Art. Circuit boards (often referred to as “printed circuit boards,” “wiring boards,” or “printed wiring boards”) are used in electronic devices to mechanically hold and to provide electrical communication between the electrical components thereof. Electrical components such as transistors, resistors, and capacitors may be soldered into a circuit board and electrically interconnected by electrically conductive signal traces formed within or on the surfaces of the circuit board. Semiconductor chips, semiconductor chip packages, and semiconductor chip modules may be provided that include a number of pins, which may be inserted into corresponding holes in the circuit board and soldered in place. Such chips, packages, and modules may include, for example, microprocessors, dynamic random access memories (DRAMs), static random access memories (SRAMs), and application specific integrated circuits (ASICs), and may each have hundreds or thousands of electrically conductive terminals requiring electrical interconnection with the conductive traces of a circuit board. The electrically conductive traces in the circuit board are used to interconnect the semiconductor chip devices and the electrical components.
Circuit boards generally are substantially planar and include one or more dielectric layers that include an electrically insulating material (such as, for example, ceramic-based materials, polymer-based materials, Bismaleimide Triazine (BT), FR-4 laminates, and FR-5 laminates), and two or more conductive layers. The conductive layers may include a plurality of conductive traces, and each conductive layer may be carried by or disposed between surfaces of the dielectric layers.
The layered structure of the circuit board may include at least one electrically conductive power layer (often referred to as a “voltage supply” layer or plane), at least one electrically conductive ground or bias layer, and one or more electrically conductive signal layers that include electrically conductive traces. For example, one or more signal layers may include conductive traces generally extending in a first direction, and one or more signal layers may include conductive traces generally extending in a second direction that is substantially orthogonal to the first direction. Additional signal layers may also be provided that include conductive traces generally extending at an angle to the conductive traces of the other signal layers.
Other relatively smaller circuit boards may be used in, for example, semiconductor die packages to redistribute the pattern of the bond pads on a semiconductor die attached to a first side of the circuit board to a different pattern of electrical contacts on the same and/or an opposite side of the circuit board. Such circuit boards may also have a layered structure, and the conductive traces may have a custom pattern configured for the particular semiconductor die or package in which they are used.
To provide electrical communication between the electrical devices and components through a circuit board, it may be necessary to provide electrical communication between conductive traces in two or more distinct layers of the circuit board. Electrically conductive vias that extend through the thickness of at least one dielectric layer of the circuit board are typically used to provide electrical communication between the conductive traces of different layers or planes of the circuit board. A conductive via typically includes a hole at least partially penetrating the circuit board. After forming the hole (by drilling, etching, or other known technique), conductive material is provided in the hole. A conductive trace on a first signal layer and a conductive trace on a second, distinct signal layer may each be electrically coupled with the electrically conductive material provided in the via. The conductive traces communicating with one another through the conductive via may be formed or provided on the circuit board either prior or subsequent to forming the conductive via in the circuit board.
Conductive vias also are used to provide electrical paths through many other types of substrates including, for example, semiconductor dice and interposer substrates.
Differential signaling processes may be used in applications requiring extremely high-speed signal transmission and processing. Differential signals are signals that are referenced to each other rather than to ground. As such, differential signaling requires two electrically conductive traces for each electrical signal. The electrically conductive traces are routed together from a driving or transmitting device to a receiving device, which subtracts the two signals from each other to recover the original signal. One trace is used to carry a “true signal phase” and a second trace is used to carry a “complementary signal phase.” Furthermore, the conductive traces that carry the true signal phase and the complementary signal phase are typically routed physically close to one another and have the same or substantially the same physical length.
FIG. 1 illustrates a portion of a circuit board 10 that includes a first conductive trace 12 extending to a first conductive via 16, and a second conductive trace 14 extending to a second conductive via 18. As illustrated, the conductive vias 16, 18 may have a diameter D0 (or other cross-sectional dimension) that is greater than a width W of each of the conductive traces 12, 14. As a result, the conductive traces 12, 14 “fan-out” from one another in a region 20 proximate the conductive vias 16, 18. In this configuration, the distance 22 separating the conductive vias 16, 18 differs from the distance 24 separating the conductive traces 12, 14 in all other regions in which they extend parallel to one another. As a result of this increased spacing between the first conductive trace 12 and the second conductive trace 14, a “return path discontinuity” may be provided or generated by the conductive vias 16, 18 when the conductive traces 12, 14 are used to carry differential signals, which may contribute to noise or otherwise degrade the electrical signals carried by the conductive traces 12, 14.
A need exists for conductive vias, structures, and other features that maintain a constant distance between corresponding or complementary conductive paths or traces as they extend from one plane in a substrate to another plane in the substrate.